1. Field of the Invention
The present invention relates to a method of processing a substrate, a post-chemical mechanical polishing cleaning method, and a method of and program for manufacturing an electronic device, and in particular relates to a method of manufacturing an electronic device according to which the flatness of a surface is improved by carrying out plasma-less etching after polishing a conductive film formed on the surface by chemical mechanical polishing.
2. Description of the Related Art
In a method of manufacturing an electronic device in which an electronic device is manufactured from a silicon wafer (hereinafter referred to merely as a “wafer”), a lithography step of forming a photoresist layer in a desired pattern on an insulating film that has been formed on a surface of the wafer, an etching step of fabricating a conductive film into gate electrodes, or fabricating wiring grooves or contact holes in the insulating film, with plasma using the photoresist layer as a mask, a film formation step of using PVD (physical vapor deposition) or the like to form a conductive film on the surface of the insulating film in which the wiring grooves or contact holes have been fabricated, and a flattening step (etch back step) of removing the formed conductive film, thus revealing the insulating film, and flattening the surface of the revealed insulating film are repeatedly implemented in this order.
In recent years, in the flattening step, a wafer surface polishing method known as CMP (chemical mechanical polishing) has come to be used instead of conventionally used dry etching or thermal reflow. In CMP, as shown in FIG. 11, the wafer is pushed against a rotating table 201 having a polishing cloth 200 made of polyurethane or the like stuck thereon by a head (wafer holding portion) 202 such that a surface of the wafer comes into close contact with the polishing cloth 200, a polishing agent (slurry) having silica (SiO2) as a principal component thereof is supplied onto the polishing cloth 200 from a slurry supply nozzle 203, and a cleaning liquid is supplied, and at the same time the rotating table 201 and the head 202 are rotated independently to one another, thus polishing the surface of the wafer. In CMP, it is thought that the polishing is promoted through a synergistic effect between physical contact between SiO2 particles in the polishing agent and a conductive film or insulating film on the wafer surface, and chemical reaction between the SiO2 particles and the conductive film or insulating film (see, for example, Japanese Laid-open Patent Publication (Kokai) No. H9-251969.
Moreover, in recent years, to prevent a decrease in signal transmission speed due to the high dielectric constant of interlayer insulating films, which has become a conspicuous problem as the wiring rule (required dimension) for electronic devices has been made smaller, low relative dielectric constant (low-κ) materials (see Table 1) have come to be used as interlayer insulating film materials. In particular, because copper is widely used as a wiring material, recently carbon-doped SiOC type low dielectric constant materials have come to be used as low dielectric constant interlayer insulating film materials. Moreover, the use of porous materials having a yet lower dielectric constant has also been investigated. Here, a relative dielectric constant of not more than 3.0 is referred to as a “low dielectric constant”.
TABLE 1RelativedielectricInterlayer insulating filmconstantStructureInorganicHSQ  3 to 2.8 Porous silica2.4 to 1.8—OrganicSiOC2.9 to 2.7 Porous SiOC2.5 to 2.2— MSQ2.9 to 2.7 Porous MSQ2.5 to 1.8—OrganicpolymersPolyimide3.5 to 3   BARERIN etc.  3 to 2.2 Teflon (registeredtrademark) etc.2.4 to 2   Amorphous carbon (F added)<2.5—
However, on the surface of an insulating film revealed by CMP, residue (shavings) of the insulating film arises due to erosion (caused by the polishing) of the insulating film on wiring due to a difference in the polishing characteristics of the insulating film depending on the density of the wiring pattern under the insulating film, and a reaction product between the SiO2 particles and the constituent material of the insulating film also arises.
Moreover, for an interlayer insulating film made of a porous material, the mechanical strength is low and adhesion to a conductive film is weak due to the many voids in the interlayer insulating film, and hence if the wafer is pushed by the head 202 at a normally used pressure in the CMP, then breaking away of the interlayer insulating film from the conductive film or disintegration of the interlayer insulating film occurs. To counteract this, in the case of using a porous material as an interlayer insulating film material, the wafer must be pushed at a low pressure, for example a pressure of not more than approximately 1.0 kPa, but with such low pressure CMP, the interlayer insulating film cannot be polished sufficiently, and hence unpolished portions arise on the surface of the interlayer insulating film polished by the CMP.
Such residue, reaction product, and unpolished portions (hereinafter referred to collectively as “polishing remnants”) on the surface of an insulating film are a causal factor in abnormalities in the inter-layer capacitance of a capacitor, or the wiring resistance, in an electronic device manufactured from the wafer, and must thus be removed.
Moreover, in the case of using CMP to polish away a conductive film that has been formed on a low dielectric constant interlayer insulating film, the revealed low dielectric constant interlayer insulating film is chemically damaged due to the low dielectric constant interlayer insulating film absorbing moisture due to contact between the surface of the low dielectric constant interlayer insulating film and the slurry or cleaning liquid used in the CMP, whereby a surface damaged layer (damaged layer) having a reduced carbon concentration is formed on the surface of the low dielectric constant interlayer insulating film.
Such a surface damaged layer has similar properties to SiO2 (the native oxide), undergoing volume shrinkage in a subsequently implemented heat treatment step, which causes voids to be produced in the insulating film. It is thus necessary to remove the surface damaged layer before implementing such a subsequent step.
As a process for removing such a surface damaged layer and polishing remnants from the surface of an insulating film, a cleaning process is known in which the surface of the insulating film is cleaned using a post-CMP cleaning liquid comprised of a quaternary ammonium hydroxide, a polar organic amine, or the like.
However, such a cleaning process uses a liquid chemical and is thus categorized as a wet etching process. The surface damaged layer and polishing remnants are thus readily dissolved by the cleaning liquid in the cleaning process, and hence there is a problem that it is difficult to control the amount removed of the surface damaged layer and polishing remnants. Here, if the surface damaged layer and polishing remnants are dissolved too much by the cleaning liquid, then copper wiring disposed under the insulating film will be revealed, and hence the copper wiring will be corroded by the cleaning liquid.